The PicoRing, designed by University of Tokyo researchers, is a ring that’s a full-fledged computer mouse when worn on your finger. Just put it on and your hand becomes the interface. Early testing shows it can do accurate scrolling and clicking with your thumb against your index finger and uses so little power that one charge lasts weeks. Engineers faced a tough problem from the start: how to put mouse intelligence into something as thin as a ring without continuous recharging.